Implantable neuromodulation systems have proven therapeutic in a wide variety of diseases and disorders. Pacemakers and Implantable Cardiac Defibrillators (ICDs) have proven highly effective in the treatment of a number of cardiac conditions (e.g., arrhythmias). Spinal Cord Stimulation (SCS) systems have long been accepted as a therapeutic modality for the treatment of chronic pain syndromes, and the application of tissue stimulation has begun to expand to additional applications such as angina pectoralis and incontinence. Deep Brain Stimulation (DBS) has also been applied therapeutically for well over a decade for the treatment of refractory chronic pain syndromes, and DBS has also recently been applied in additional areas such as movement disorders and epilepsy. Further, in recent investigations, Peripheral Nerve Stimulation (PNS) systems have demonstrated efficacy in the treatment of chronic pain syndromes and incontinence, and a number of additional applications are currently under investigation. Furthermore, Functional Electrical Stimulation (FES) systems, such as the Freehand system by NeuroControl (Cleveland, Ohio), have been applied to restore some functionality to paralyzed extremities in spinal cord injury patients.
These implantable neuromodulation systems typically include one or more electrodes carrying stimulation leads, which are implanted at the desired stimulation site, and an implantable neuromodulation device (e.g., an implantable pulse generator (IPG)) implanted remotely from the stimulation site, but coupled either directly to the neuromodulation lead(s) or indirectly to the neuromodulation lead(s) via a lead extension. The neuromodulation system may further comprise a handheld external control device (e.g., a remote control (RC)) to remotely instruct the neuromodulator to generate electrical stimulation pulses in accordance with selected stimulation parameters.
Implantable neuromodulation devices are active devices requiring energy for operation, and thus, the neuromodulation system oftentimes includes an external charger to recharge a neuromodulation device, so that a surgical procedure to replace a power depleted neuromodulation device can be avoided. To wirelessly convey energy between the external charger and the implanted neuromodulation device, the charger typically includes an alternating current (AC) charging coil that supplies energy to a similar charging coil located in or on the neuromodulation device. The energy received by the charging coil located on the neuromodulation device can then be stored in a rechargeable battery within the neuromodulation device, which can then be used to power the electronic componentry on-demand. Depending on the settings, the neuromodulation device may need to be recharged every 1-30 days.
Electrical stimulation energy may be delivered from the neuromodulation device to the electrodes in the form of an electrical pulsed waveform. Thus, stimulation energy may be controllably delivered to the electrodes to stimulate neural tissue. The configuration of electrodes used to deliver electrical pulses to the targeted tissue constitutes an electrode configuration, with the electrodes capable of being selectively programmed to act as anodes (positive), cathodes (negative), or left off (zero). In other words, an electrode configuration represents the polarity being positive, negative, or zero. Other parameters that may be controlled or varied include the amplitude, width, and rate of the electrical pulses provided through the electrode array. Each electrode configuration, along with the electrical pulse parameters, can be referred to as a “stimulation parameter set.”
With some neuromodulation systems, and in particular, those with independently controlled current or voltage sources, the distribution of the current to the electrodes (including the case of the neuromodulation device, which may act as an electrode) may be varied such that the current is supplied via numerous different electrode configurations. In different configurations, the electrodes may provide current or voltage in different relative percentages of positive and negative current or voltage to create different electrical current distributions (i.e., fractionalized electrode configurations).
As briefly discussed above, an external control device can be used to instruct the neuromodulation device to generate electrical stimulation pulses in accordance with the selected stimulation parameters. Typically, the stimulation parameters programmed into the neuromodulation device can be adjusted by manipulating controls on the external control device to modify the electrical stimulation provided by the neuromodulation device system to the patient. Thus, in accordance with the stimulation parameters programmed by the external control device, electrical pulses can be delivered from the neuromodulation device to the stimulation electrode(s) to stimulate or activate a volume of tissue in accordance with a set of stimulation parameters and provide the desired efficacious therapy to the patient. The best stimulus parameter set will typically be one that delivers stimulation energy to the volume of tissue that must be stimulated in order to provide the therapeutic benefit (e.g., treatment of pain), while minimizing the volume of non-target tissue that is stimulated.
However, the number of electrodes available, combined with the ability to generate a variety of complex stimulation pulses, presents a huge selection of stimulation parameter sets to the clinician or patient. For example, if the neurostimulation system to be programmed has an array of sixteen electrodes, millions of stimulation parameter sets may be available for programming into the neurostimulation system. Today, neurostimulation system may have up to thirty-two electrodes, thereby exponentially increasing the number of stimulation parameters sets available for programming.
To facilitate such selection, the clinician generally programs the neuromodulation device through a computerized programming system. This programming system can be a self-contained hardware/software system, or can be defined predominantly by software running on a standard personal computer (PC). The PC or custom hardware may actively control the characteristics of the electrical stimulation generated by the neuromodulation device to allow the optimum stimulation parameters to be determined based on patient feedback or other means and to subsequently program the neuromodulation device with the optimum stimulation parameter set or sets. The computerized programming system may be operated by a clinician attending the patient in several scenarios.
For example, in order to achieve an effective result from SCS, the lead or leads must be placed in a location, such that the electrical stimulation will cause paresthesia. The current understanding is that paresthesia induced by the stimulation and perceived by the patient should be located in approximately the same place in the patient's body as the pain that is the target of treatment. If a lead is not correctly positioned, it is possible that the patient will receive little or no benefit from an implanted SCS system. Thus, correct lead placement can mean the difference between effective and ineffective pain therapy. When electrical leads are implanted within the patient, the computerized programming system, in the context of an operating room (OR) mapping procedure, may be used to instruct the neuromodulation device to apply electrical stimulation to test placement of the leads and/or electrodes, thereby assuring that the leads and/or electrodes are implanted in effective locations within the patient. However, despite location of paresthesia in the location of the pain, not all SCS effectively treats pain. There, thus, remains a need for alternative SCS treatment locations on a patient's body.
Once the leads are correctly positioned, a fitting procedure, which may be referred to as a navigation session, may be performed using the computerized programming system to program the external control device, and if applicable the neuromodulation device, with a set of stimulation parameters that best addresses the painful site. Thus, the navigation session may be used to pinpoint the volume of activation (VOA) or areas correlating to the pain. Such programming ability is particularly advantageous for targeting the tissue during implantation, or after implantation should the leads gradually or unexpectedly move that would otherwise relocate the stimulation energy away from the target site. By reprogramming the neuromodulation device (typically by independently varying the stimulation energy on the electrodes), the volume of activation (VOA) can often be moved back to the effective pain site without having to re-operate on the patient in order to reposition the lead and its electrode array. When adjusting the volume of activation (VOA) relative to the tissue, it is desirable to make small changes in the proportions of current, so that changes in the spatial recruitment of nerve fibers will be perceived by the patient as being smooth and continuous and to have incremental targeting capability.
One known computerized programming system for SCS is called the Bionic Navigator®, available from Boston Scientific Neuromodulation Corporation. The Bionic Navigator® is a software package that operates on a suitable PC and allows clinicians to program stimulation parameters into an external handheld programmer (referred to as a remote control). Each set of stimulation parameters, including fractionalized current distribution to the electrodes (as percentage cathodic current, percentage anodic current, or off), may be stored in both the Bionic Navigator® and the remote control and combined into a stimulation program that can then be used to stimulate multiple regions within the patient.
Although alternative or artifactual sensations, known as paresthesia, are often appreciated by patients, patients sometimes report these sensations to be uncomfortable, and therefore, they can be considered an adverse side-effect to neuromodulation therapy in some cases. It has been shown that the delivery of sub-threshold electrical energy (e.g., high-rate pulsed electrical energy and/or low pulse width electrical energy) can be effective in providing neuromodulation therapy for chronic pain without causing paresthesia.
A patient's physiological midline is a line of electrical field positions (i.e., loci) on the patient's body where the effect of the stimulation (e.g., paresthesia) is felt symmetrically or equally on both sides of the patient's body. However, the physiological midline varies from patient to patient and does not necessarily coincide with the anatomic midline. Further, it is difficult to immediately determine if the sub-threshold neuromodulation therapy is delivered to the physiological midline of a patient, because there is a lack of paresthesia that may otherwise indicate that the electrical field is being delivered to the physiological midline of a patient. There, thus, remains a need to provide a neuromodulation system that is capable of delivering sub-threshold neuromodulation therapy to the physiological midline of a patient.